Machine tool transmission



1939- M. MARTELLOTTI ucmm TOOL mmsmssou Filed March 26, 1936 W L v ATTORNEY.

patenta Aug. '22, 1939 I I z,7o,502

UNITED' STATES PATENT .OFFICE u 2,70,502 MACHINE TOOL TRANSMISSION Mario Martellotti, Cincinnati, Ohio, 'assignor to The Cincinnati Milling Machine Co., Cincinnati, Ohio, a co-poration of Ohio Application March 26, 1936, Serial No. 70,988

` Claims. (c. 74 19) This invention relates to machine tools and less of whether the power transmitting band is more particularly to an improved variable speed a deformable or non-deformable type. transmission therefor. This invention contemplates the use of a variv One of the objects of this invention is to make able speed friction device utilizng a power trans- 5 possible the use of a variable speed friction demitting band of the non-deformable type, such a vice in machine tool drives having large power as a metallic ring. In such a devicefor-every variations for any given speed. 'variation of load, the ring automatically changes Another object of this invention is to provide its position in such a, manner as to increase the a transmission having a variable speed friction pressure of contact between the ring and the 10 device for obtaining rate changes, which is apdriving and driven cones. If such a device were 10' plicable to machine tool drives having a large utilized in drives having continuous power variapower variation for any given speed, without tion, there would be set up a tangential oscillacausing excessive wear on the device. tion of the ring accompanied by sudden increase Other objects and advantages of the present and decrease of the contatual pressure, which invention should be readily apparent by referwould cause excessive wear and very shortly ren- 15 ence to the following specification, considered in der the device useless for practical purposes. conjunction with the accompanying drawing In this invention' there has been contrived a forming a part thereof and it is to be understood transmission in which the various elements are that any modifications may be made in the exact arranged in a predetermined succession or order,

structural details there shown and described, whereby the life of the variable speed friction 20 within the scope of the appended claims, without device is materially lengthened. i

departing from or exceeding the spirit of the One instance of a driven member which will invention. cause the power requirement to vary for a given Referring to the drawing in which like referspeed thereof is the cutter spindle of a milling ence numerals indicate like or similar parts: machine, and 'especially when utilized to rotate 25 Figure 1 is a sectional View in elevation of a a slotting cutter which has straight teeth unitransmission embodying the principles of this formly spaced around its periphery. These teeth invention. intermittently engage the work and cause a Figure 2 is a fragmentary View showing t rapid rise and fall in the power requirement.

Variable p d friction device in p and e such a tool spindle is indicated bythe reference 30 means for coupling it to a prime mover. V numeral Io in Figure 1 of the drawing and this It is recognized that variable speed friction spindle is supported by an'ti-friction bearings ll devices have been used to a limited extent in and |2 which may be mounted in a carrier 13 i e too s and other forms of achi ery, b which is adjustable relative to a fixed support I4 usually the applications have been confined to The spindle may have a splined connection as a't instances Wherein Power demand s b a a y l5 to a. bull gear IS which drives the same but is uniform. Because of the inherent nature of a held against axial movement by the thrust bearfriction drive Of any yp they e regarded as ing !2. This permits the forward portion of the unsuitable where the power demand varies interspindle to be attached to a quill IT, whereby the 40 mittently over a wide range for any given speed. cutter spindle may be axially adjusted without 40 In the 'conventional belt drive, for instance, breaking its driving connection. the portion of the belt that lies to one side of For th purpose of varying the rate of rotation the D y and which transmits thedriving force of the spindle, a variable speed friction device is is known as the tight side of the belt, and the utilized which may be the same as that shown remaining po t o on th ot r i of th p l y in U. s. Patent 1,95o,675, filed October 15, 1931, 45 is known as the slack side of the belt. When the d i sued March 13, 1934, to D. H. Heynau. load increases without change of speed, the tight hi d i comprises mainly a fi t, pair of side is put under greater tension and the belt perd friction discs s and s, as shown in Fjggrips the pu eys te tightly- Thiis, a Sort ure 2, and a second pair of tapered friction discs readiustment occurszo .and 2, as shown in Figure 1, and a metallic If the power reqi emen i ter ttent y rring 22 passes around these discs and is always creases and decreases in rapid succession, it will in driving contact therewith'. Variations in rate be apparent that oscillations will be set up in the are obtained by simultaneously adjusting the disc belt due to variations in tension in the tight side s toward the. disc !9 and the disc. ZI away from of the belt. 'This phenomena will occur regardthe disc 20 or vice versa. 55

that' longitudinal movement between them may be efi'ected by relative rotation between them, and thus longitudinal movement of the tapered cone associated therewith.

Since all of these parts are of metal, it is apparent that if vibration is set up in the ring 22 that the parts would be literally pounded to pieces in a short time. To obviate these deleterious efiects, this device has been connected in a definite serial relation to the remaining parts of the transmission and means are provided whereby the vibrations caused by the intermittent action of the cutter are absorbed before they reach the variable speed device. To this end, the drive shaft 23 of the variable speed friction device, indicated generally by the reference numeral 24, is connected by suitable power transmitting means. such as the chain 25 and sprocket wheels 26 and 21, to a prime mover 28. When the prime mover is running, it continuously actuates the vaiable speed device and its output shaft 29. The shaft 29 supports for free rotation a pair f bevel gears 30 and 3i which intermesh with a common bevel gear' 32 secured to the end of shaft 33. This shaft drives bevel gear 34, which intermeshes with gear 35 secured to the shaft 36. This shaft has a pinion 31' secured thereto which drives the bull gear IE.

A double cone friction clutch 38 splined on the shaft 29 is adapted to be shifted by'the fork 39 to selectively engage the friction cone 40 integral with bevel gear 30, or the friction cone 4| integral with the bevel gear 3| for driving the shaft 33, and. thereby the spindle in opposite directions. This clutch may also be moved to a. central position, a`s shown in Figure 1, for stopping rotation of the cutter spindle.

In order to prevent vibration's of the cutter spindle from being transmitted to the variable speed friction` device, a flywheel 42 is attached tothe end of shaft 29, and this flywheel should be made sufliciently large and have sufficient mass to produce the necessary inertia eflfects to equalize the load on the output shaft of the friction device and thus minimize oscillations of the ring to a practical degree. In order to obtain the desired results it is to be noted that 'the prime mover is connected in a substantially one to one ratiowith the variable friction device whereby the output shaft 29 will have a relatively high speed, and that the flywheel is attached to this output shaft whereby the fiywheel will also have a relatively high rate of rotation and thereby be more efiective in accomplishing the purposes for which it is intended. From this point on to the spindle, the. gearing is so arranged that there is a series of reductions efiected so that the final rates of rotation of the cutter spindle' ill are not any greater than those conventionallyemployed in presentd-aymachines. In other words, there is a first reduction effected between bevel gears 30, 3l and the driven gear 32; between the driving bevel gear 34 and the' driven bevel gear 35; and between the driving pinion 31 an dthe bull gear lE.

It will thus be seen that an improved variable speed transmission has been provided for a machine tool element which inherently creates a variable power demand, comprising a variable speed friction device which is directly coupled to a prime mover for a relatively high rate of rotation, and that the output shaft of the device has directly connected thereto a flywheel, whereby the best inertia efiects can be obtained and that this output shaft is connected through a reduction train to the spindle in order that conventional speed rates thereof may be obtained in spite of the fact that the first portion of the transmission' is driven at a higher rate than is usual in such cases.

What is claimed is:

1. In a. spindle transmission for a milling machine, the combination of a prime mover, a variable speed friction device comprising a first pair of co-axial metallic conical discs, motion transmitting means coupling said discs to the prime mover for actuation thereby, a second pair of coaxial metallic conical discs, a metallic friction ring circumscribing said discs and in frictonal engagement therewith for transmitting motion spindle adapted to actuate a cutter having a natural period of vibration during cutting, reduction gearing connecting said shaft for rotation of the spindle whereby said shaft will always rotate at a greater rate than said spindle, and means attached to said shaft for preventing tangential oscillation of said metallic ring relative to said driven discs and thereby prevent deformation of the conical surfaces of said driven discs. v

2. In a spindle transmission for a milling machine, the combination with a cutter spindle adapted to drive a cutter having a natural period of vibration, of a prime mover, a first shaft having a pair of co-axial metallic conical discs fixed therewith, a power transmitting band coupling the shaft to the prime mover, a second shaft having a driven pair of co-axial metallic conical discs supported thereon, a metallic friction ring circumscribing said discs and in frictional engagement therewith, means to adjust one pair oi' said discs axially away from one another and the other pair of discs axially toward one another to vary the rate of rotation of said driven discs, reduction gearing connecting the final shaft to said spindle whereby said shaft will rotate at a greater rate than said spindle, and means associated with said final shaft to prevent oscillation 'of said spindle from causing tangential oscillation of said ring relative to the drivenpair of said discs and thereby prevent mutilation of the conical surfaces of said driven discs.

3. In a milling machine transmisson, the com- 4 tallic ring circumscribing said discs, means to efiect relative adjustment between the pairs of discs to vary the speed 'of rotation of said final shaft, a reduction gear train extendng to said spindle, a reversing mechanism coupling said final shaft to said gear train, and means attached to said final shaft for preventing vibration of the spindle from causing tangential oscillation of the 'discs supported on said final shaft, a 'rigid memetailic ring relative to the discs carried by said final shutt.

4. In a transmission tor driving a toothed cutter actuating spindle of a miliing machine through a rate changer of the stepless variety, comprising pairs oi' conical dis'cs and a rigid connecting member, the combination with a prime mover of means ior oonnecting the rate changer A ger to the first pair of said disc for actuation at a reiativeiy !ast rate, a shaft having the second pair ot said discs rigidlyconnected thereto, speed reduction gearing connecting the shaft for actuation ot the spindle whereby the spindle wiil always rotate at a slower rate 'than said shaft, and means attached to said shaft to prevent spindie vibration created -by said toothed cutter from causing saidvrigid member to rapidly and inter-'- mittently grip the surfaces of said driven oones and causing mutilation of the contactual surfaces thereof.

5. In a transmission for driving a toothed cutter actuating spindle of a milling machine through a stepless rate changer of the variety consisting of spaced pairs of conical discs and a rigid friction connecting member, the combina-' 'thereof at a relatively rast rate, a supporting shaft for the driven pair of discs, means to inversely change the spacing between the respective pairs of discs to eiIect stepless changes in the rate of rotat'ion of the spindle, speed reduction gearing connecting said shaft to the spindle, including a reversing mechanism, and means attached to said shalt to prevent spindle vibration created by said toothed cutter from causing rap-.

id vibration of the driven discs relative to the rigid driving member regardless of the direction of rotation of said spindie, whe-eby` rapid deformation of the surfaces of the driven pair of conical discs will be prevented.

MARIO mmm''n. 

